1. Field of the Invention
The present invention relates to access-control apparatus including a device comprising an array of selectively-actuable keys for the entry of authorisation or identification data represented as a sequence of characters. The invention is in particular concerned with the secure inputting of identification or authorization data comprising a sequence of digits and/or letters where, for example, it is necessary to enter a secret code of this kind into an identification device in order to unlock a safe or strongroom, gain admission to a building, use a cash dispensing machine, log-on to a computer network, or obtain access to some other service, and it is an aim of the invention to provide a data entry device suitable for such service which can be operated in such a manner as to make it impractical for an unauthorised person to discover or reproduce the entered data by observing the positions of the actuated keys during the data-entry process and/or inspecting the array of keys afterwards.
2. Background of the Invention
In a conventional keypad as used for the entry of authorisation or identification codes for access-control purposes, there is an array of keys to each one of which is permanently assigned a respective numeric character 0-9, and usually one or more specific "function" keys. From a security standpoint, however, there are certain disadvantages in a fixed character-to-key assignment. Firstly, in cases where there is repetitive legitimate entry of a given code, for example in a code-recognition safe or strongroom door lock, it may be possible for an unauthorised person to gain information on the composition of that code by studying the wear pattern of the keys, or even "fingerprinting" the keys.
Furthermore, a bystander who observes a person entering a code may be able to recognise, and make fraudulent use of, that code simply by noting the position and order of the keys being actuated. In order to overcome these problems it is known, eg from U.S. Pat. Nos. 4,333,090 and 4,502,048, to assign the characters to the keys electronically in a random pattern and to change the random pattern after each successive actuation or series of actuations of the keys, with the assigned key values at any one time being displayed in relation to the keys preferably in a manner to be seen only by the person who is actually operating them. With this arrangement all of the keys will tend to be used and worn at a similar rate whatever the composition of the code(s) commonly entered. Furthermore, a bystander who observes the actuation of a series of keys but cannot see the assigned key values at that time will not be able to determine the code entered thereby because there is no permanent relationship between the keys and their characters.
While this "randomizing" of the character-to-key assignment provides useful protection against surreptitious reading of entered data it does have a drawback of its own. That is to say the very nature of the changing random pattern of characters can make it difficult for a person using the device legitimately to locate the specific character he wishes to enter at any one time, thereby increasing the time taken to enter the code and the probability of an incorrect entry being made.